You nod without hesitating. Marisa might have ruined your life with a transformation, making it impossible for you to ever be David again. At the same time, though, she seemed as shocked as you were and did everything she could to help. Making you younger... you had not wanted, but now you can't even remember /why/ you didn't want it. You feel much calmer now than you were before. All those classes and friends and appointments you had as David still bother you if you think about them, but seem to fade away when you don't. It's much more fun to think of the castle and living with the woman that feels far more like a sister than anything else.
She smiles at your reaction, patting you gently on the head with one hand before pulling across the drawbridge of the smaller castle, raising it behind her with a click of the garage door opener on the roof of the car. You're in a daze as you're led inside, past an entirely period medieval great hall with an absurd-looking kitchen of modern appliances set up at the far end. Up a huge spiral staircase you go, past a long hallway filled with portraits of Marisa's relatives. She has a story for every one... and almost all of them seem to be women. You wonder who all the fathers are and why they aren't pictured here, but... you're much too nervous to ask. Near the end of the hall is Marisa's portrait, which like all the others is a tasteful artistic nude. In her case, she's leaning sideways against an apple tree, with a big black cat in the foreground between you and her thighs. Her breasts are exposed, but you almost don't notice. It's only the similarities in color between her nipples and the apples hanging next to them that attracts your eyes. Then you remember you're looking at her /naked/, and you blush, your knees buckling together to try and... you're not sure really. You don't get to be flustered for long, because it seems you've got a portrait here already. How you could you have no idea, but there you are on the swing you saw outside, grinning energetically as you zoom upward. You whimper at how much of you is exposed: way more than Marisa.
"It's no fair! I'm not really your sister!" You protest, looking away from the little round painting and up at your guardian, though not far. "It's not okay to have everyone naked like this! It's... It's... weird!"
"It's an old family tradition," Marisa explained, as though that settled the issue. "And if you're not my sister, I dunno who is. You look just like me... you've got a spark of /my/ magic in you. That means we're related far more than blood ever could if you ask me." She hurries you on past the end of the hallway, through a huge set of double doors. It's a royal bedroom of exquisite luxury, though modern objects are juxtaposed at random. The solar is filled with college-looking textbooks and a laptop, there's a plasma TV mounted about the fireplace... but you don't stay. There are stairs in here, and up them you're led to a hallway of smaller bedrooms.
"For the ladies-in-waiting," explained Marisa as she opens one of the doors. It looks... like the room of a modern tweenage girl, pink and yellow in great abundance. The bed's covered in various plushies, the walls in posters of Justin Bieber and the like. There's a shelf and a desk too, stocked with old-looking books and other supplies, which look musty and boring compared to the rest of the room." This will be your room while you're under eighteen. Once you're an adult, you /could/ move out... but you don't have to pay rent with me, so I bet you won't." Marisa leads you to a dresser, opening it and pulling out a soft green nightgown. She holds it to her face for a moment, grinning. "This used to be mine too, when I was your age. It'll be a little high on you, but... that doesn't really matter with a nightgown. And here..." Another drawer, and she draws out a soft green pair of panties and a training bra clearly meant for girls your age without anything to actually support. "Do you want my help getting read for bed? There's an awful lot of magic in here... I could show you some of it!"
Before you realize what you're doing, your familiar climbs the rest of the way onto your head and squeaks to Marisa. The strangest thing is that the ferret talks in your voice, not his, and you find yourself agreeing with him... you... right away. "We want time to recover please! We can put ourselves to bed..."
Marisa frowned, then shrugged. "Alright, David." She hugs you one last time. "Don't stay up too late! It's your first day as my apprentice... running a magic shop is hard work! Don't think you won't have to help just because you're little!" Then she departs, and the door clicks closed behind her. You're left alone then, except for the soft brown eyes of your familiar, who jumps down onto the bed atop the panties to look up at you expectantly. At last you're on your own. You have this whole room to explore, maybe even the whole castle. Of course, that's not the only thing you could do. After a moment of consideration, you decide to...